The present invention relates to a multilayer optical disc having a plurality of recording reproduction surfaces, a method and a device for recording optical information in this multilayer optical disc.
A conventionally known multilayer optical disc capable of recording on and reproducing from a plurality of recording reproduction surfaces is described, for example, in JP 10(1998)-505188A.
In the following, the structure of a conventional multilayer optical disc will be explained by referring to the drawings. FIG. 7 is a cross-sectional view showing a conventional optical disc 10 taken in the direction perpendicular to the track direction. In addition, for simplifying the explanation, an optical disc of a double layer structure will be used.
As shown in FIG. 7, a guiding groove 7 for tracking (alternatively, an address signal recorded in advance and formed as a pit) is formed on one surface side of a first substrate 1, and further on this surface, a recording reproduction film for partially reflecting and partially transmitting an optical beam 8 entering the first substrate 1, focused by an objective lens 9, is formed to create a first recording reproduction surface 3. Furthermore, a guiding groove 6 for tracking (alternatively, an address signal recorded in advance and formed as a pit) also is formed on the surface of a second substrate 2, and a recording reproduction film for reflecting the optical beam 8 passing through the first recording reproduction surface 3 is formed to create a second recording reproduction surface 4. Furthermore, a separating layer 5 is interposed to separate the first recording reproduction surface 3 and the second recording reproduction surface 4 and to bond them together.
However, the multilayer structure as mentioned above (double layer structure in the conventional example) suffers from the following problem when the bonded state in the cross-sectional view taken perpendicular to the aforementioned cross-sectional view, that is in the track direction, is as that shown in FIG. 8.
In addition, for explanatory purposes, FIG. 8 expresses the actual sector structure (shown in FIG. 9(b)) of a multilayer optical disc, which is shown as a plan view in FIG. 9(a), in the form of a schematic sector structure for each recording reproduction surface.
FIG. 9(b) is, as shown in FIG. 9(a), an enlarged view of the vicinity of an address area 92 in a certain track among a group of tracks 91 formed as concentric circles or spirally in the multilayer optical disc, and shows a part of a groove portion 93 in the (nxe2x88x921)th sector, an address pit portion 941 corresponding to an address area of the nth sector to be described later, and a part of a groove portion 942 in the following nth sector 94. This groove portion, expressed in the form of a schematic sector structure, is divided into a gap area and a data area to be described later.
Moreover, the constituent elements shown in FIG. 7, i.e. the first substrate 1, the second substrate 2 and the separating layer 5 are omitted in FIG. 8 for explanatory purposes.
In FIG. 8, 31 is a first recording reproduction surface, and 41 is a second recording reproduction surface. 311, 312 and 313 respectively are an address area, a data area and a gap area for dividing the address area 311 and the data area 312 in the first recording reproduction surface 31. Moreover, 411, 412 and 413 respectively are an address area, a data area and a gap area for dividing the address area 411 and the data area 412 in the second recording reproduction surface 32.
The gap areas 313, 413 are provided to perform a signal processing, when a recording and a reproduction for a multilayer optical disc are performed by a drive, by clearly separating a reproduced address signal and a reproduced data signal of a data area, and by avoiding the gap areas 313, 413, the recording operation is performed respectively for the first recording reproduction surface 31 and the second recording reproduction surface 41.
However, as shown in FIG. 8, when the heads of the address areas 311 and 411, that is, the front positions of sectors are bonded together by a shift L1, and when this amount of shift L1 is larger than a length G1 of the gap areas 313 and 413, an area xcex941, which is an area at the rear end portion in the address area 311 of the first recording reproduction surface 31, overlaps with an area xcex942, which is an area at the front end portion in the data area 412 of the second recording reproduction surface 41, in the irradiation direction of an optical beam 81, that is, seen from above the surface. In addition, a length of the area xcex941 and that of the area xcex942 are equal to L1xe2x88x92G1.
Furthermore, the optical beam 81 passes through the area xcex941 of the first recording reproduction surface 31 and is emitted onto the area xcex942 of the second recording reproduction surface 41 to record information.
Here, when the two recording reproduction surfaces of this multilayer optical disc are made of phase change type recording reproduction films, a recording in a phase change type recording reproduction film is performed based on the principle of changing its crystal structure by irradiation of a high-power optical beam. Therefore, when the recording is preformed for the area xcex942 in the second recording reproduction surface 41, that is, for the area at the front end portion in the data area 412 of the second recording reproduction surface 41, the high-power optical beam 81 is emitted also onto the area xcex941 at the rear end portion in the address area 311 of the first recording reproduction surface 31.
Therefore, the crystal structure of the recording reproduction film formed on one part in the address area 311 of the first recording reproduction surface 31 also is affected. As a result, when the address area 311 of the first recording reproduction surface 31 is to be reproduced after completing the recording operation for the second recording reproduction surface 41, the S/N ratio of the reproduced signal is deteriorated, and the problem that the address information cannot be recognized correctly arises.
Furthermore, the example shown in FIG. 8 was explained by referring to the case where the first recording reproduction surface 31 and the second recording reproduction surface 41 were bonded together in a state in which the front position in the sector of the first recording reproduction surface 31 is shifted to the right side of the surface relative to the second recording reproduction surface 41. Similarly, also in the case where the front position in the sector of the first recording reproduction surface 31 is shifted to the left side of the surface relative to the second recording reproduction surface 41 and bonded together, the address area 411 of the second recording reproduction surface 41 is affected when a recording operation for the first recording reproduction surface 31 is performed. As a result, the S/N ratio of the reproduced signal from the address area 411 is deteriorated, and the problem that the address information cannot be recognized correctly arises.
Moreover, the conventional example was explained by referring to the case of having two recording reproduction surfaces, but also in the case of having three and more recording reproduction surfaces, a recording operation for an arbitrary recording reproduction surface affects address areas in other recording reproduction surfaces, so that the problem that this address information cannot be recognized correctly arises.
Furthermore, in the case where data are already recorded in the data areas of both recording reproduction surfaces, at the time when a recording operation is performed for one of the recording reproduction surfaces, also for the data area in the other recording reproduction surface, a high-power optical beam is emitted onto an area where the respective data areas overlap with each other (xcex943 shown in FIG. 8), so that errors arise due to the deteriorated S/N ratio of the reproduced signal. Generally, an error correction code is appended to data, so that the content of the reproduced data is restored by this function to some degree but not completely. The deterioration in the S/N ratio of the reproduced signal in this data area will be explained below more in detail.
Like FIG. 8, FIG. 10 is a diagram expressing the actual sector structure of a conventional multilayer optical disc in the form of a schematic sector structure for each recording reproduction surface. In addition, in FIG. 10, the same reference numerals are given to the same constituents as those in FIG. 8, and the explanations thereof are omitted.
First, FIG. 10(a) will be explained. FIG. 10(a) shows a state in which the first recording reproduction surface 31 is shifted in the scanning direction (to the right side of the surface) of the optical beam 81 relative to the second recording reproduction surface 41 and bonded together. In FIG. 10, a section Z1 or a section Z3 is an area where the data area 312 of the first recording reproduction surface 31 does not overlap with the data area 412 of the second recording reproduction surface 41 and corresponds to a predetermined precision at the time when the two recording reproduction surfaces are bonded together. Moreover, a section Z2 shows an area where the data area 312 of the first recording reproduction surface 31 overlaps with the data area 412 of the second recording reproduction surface 41.
When optical information (data) is already recorded in the data area 312 of the first recording reproduction surface 31, due to the fact that the optical conditions of the recording reproduction surfaces differ and that the transmittances of the optical beam 81 are different, the recording power of the emitted optical beam 81 differs in the section Z1 and in the section Z2 of the data area 412 on the second recording reproduction surface 41.
Next, FIG. 10(b) will be explained. FIG. 10(b) shows a state in which the first recording reproduction surface 31 is shifted in the direction opposite to the scanning direction (to the left side of the surface) of the optical beam 81 relative to the second recording reproduction surface 41 and bonded together. As in FIG. 10(a), the section Z1 or the section Z3 shown in FIG. 10(b) is an area where the data area 312 of the first recording reproduction surface 31 does not overlap with the data area 412 of the second recording reproduction surface 41 and corresponds to a predetermined precision at the time when the two recording reproduction surfaces are bonded together. Moreover, as in FIG. 10(a), also the section Z2 shows an area where the data area 312 of the first recording reproduction surface 31 overlaps with the data area 412 of the second recording reproduction surface 41.
Here, when data are already recorded in the data area 312 of the first recording reproduction surface 31, due to the fact that the optical conditions of the recording reproduction surfaces differ and that the transmittances of the optical beam 81 are different, the recording power of the emitted optical beam 81 differs in the section Z1 and in the section Z2 of the data area 412 on the second recording reproduction surface 41.
When the transmittance before recording is smaller than the transmittance after recording, a recording for the second recording reproduction surface 41 is performed by taking this transmittance into account. But even when the data could be recorded with an optimal recording power in the section Z2, a recording beam with an excessive power is emitted onto the portion corresponding to the section Z1 (in the case of FIG. 10(a)) or the section Z3 (in the case of FIG. 10(b)). On the other hand, when the transmittance before recording is larger than the transmittance after recording, a recording for the second recording reproduction surface 41 is performed by taking this transmittance into account. But even when the data could be recorded with an optimal recording power in the section Z2, a recording beam with a much smaller power will be emitted onto the portion corresponding to the section Z1 (in the case of FIG. 10(a)) or the section Z3 (in the case of FIG. 10(b)).
As a result, when a reproduction signal is to be obtained from the second recording reproduction surface 41, a difference in the signal amplitude of the reproduction signal may arise between the portions corresponding to the sections Z1 and Z2 (in the case of FIG. 10(a)) or the sections Z2 and Z3 (in the case of FIG. 10(b)). Thus, a difference in the S/N ratio may arise within the data area, so that a part of the data recorded in the second recording reproduction surface 41 may not be read out correctly even by using an error correction code appended to the data.
In particular, when a phase change type material is used for the recording films constructing the recording reproduction surfaces, due to the fact that its phase state changes (crystal state and amorphous state) by recording data, the difference in the transmittance before and after the recording is large, so that the problem mentioned above becomes more notable.
Therefore, it is an object of the present invention to provide a multilayer optical disc capable of reproducing an address signal and a data signal correctly even when using a multilayer optical disc that is made up of a plurality of recording reproduction surfaces bonded together in a state in which front positions in sectors of the respective recording reproduction surfaces do not match completely. Another object is to provide a method and a device for recording optical information in this multilayer optical disc.
To achieve the above object, a first multilayer optical disc of the present invention is characterized in that the multilayer optical disc has a plurality of recording reproduction surfaces having a sector structure, in which an address area and a data area recorded in advance are divided by a gap area of a predetermined length, and that the plurality of recording reproduction surfaces are bonded together such that front positions of sectors in the plurality of recording reproduction surfaces are aligned with a precision of not more than the length of the gap area.
Furthermore, to achieve the above object, a second multilayer optical disc of the present invention is characterized in that a plurality of recording reproduction surfaces having a sector structure, in which an address area and a data area recorded in advance are divided by a gap area, are bonded together with a predetermined precision with reference to front positions of the sectors, and that the length of the gap area is not less than the predetermined precision with reference to the front positions of the sectors.
Furthermore, to achieve the above object, a third multilayer optical disc of the present invention is characterized in that the multilayer optical disc includes a first recording surface and a second recording surface, each having an address area, a data area for recording information and a gap area with a predetermined length arranged between the address area and the data area, wherein an amount of displacement between a front position in the address area of the first recording surface and a front position in the address area of the second recording surface, seen from a direction of a beam emitted onto the recording surfaces for recording and reproduction of information, is smaller than the length of the gap area.
Furthermore, to achieve the above object, a fourth multilayer optical disc of the present invention is characterized in that the multilayer optical disc includes a first recording surface and a second recording surface, each having an address area, a data area for recording information and a gap area with a predetermined length arranged between the address area and the data area, wherein an amount of displacement between a back end position in the address area of the first recording surface and a back end position in the address area of the second recording surface, seen from a direction of a beam emitted onto the recording surfaces for recording and reproduction of information, is smaller than the length of the gap area.
Furthermore, to achieve the above object, an optical information recording method according to the present invention is a method for recording optical information in a multilayer optical disc including a plurality of recording reproduction surfaces formed on every layer, with a sector structure having a gap area arranged between an address area and a data area in a scanning direction of an optical beam, wherein a bonding precision L with reference to a front position in the sector of a certain recording reproduction surface and a length G of the gap area in the scanning direction satisfies a relationship of Lxe2x89xa6G for all recording reproduction surfaces. The method is characterized by the steps of detecting an amount of displacement between front positions in the sectors of other recording reproduction surfaces relative to the front position in the sector of the certain recording reproduction surface, and, based on the detected amount of displacement, determining a data recording starting position and a data recording ending position for each recording reproduction surface such that the data recording starting position and the data recording ending position of the respective sectors are matched in the plurality of recording reproduction surfaces.
In addition, in the optical information recording method of the present invention, it is preferable that the data recording starting position and the data recording ending position respectively are determined to be the starting position and the ending position in the data area of the recording reproduction surface where the front position of the sector is displaced most in a direction opposite to the scanning direction among the plurality of recording reproduction surfaces.
Furthermore, to achieve the above object, an optical information recording device according to the present invention is a method for recording optical information in a multilayer optical disc including a plurality of recording reproduction surfaces formed on every layer, with a sector structure having a gap area arranged between an address area and a data area in a scanning direction of an optical beam, wherein a bonding precision L with reference to a front position in the sector of a certain recording reproduction surface and a length G of the gap area in the scanning direction satisfies a relationship of Lxe2x89xa6G for all recording reproduction surfaces. The device is characterized in that the device includes a detection part for detecting an amount of displacement between front positions in the sectors of other recording reproduction surfaces relative to the front position in the sector of the certain recording reproduction surface, and a gate signal generation part for generating a gate signal designating a data recording ending position from a data recording starting position for each recording reproduction surface to match the data recording starting positions and the data recording ending positions of the respective sectors in the plurality of recording reproduction surfaces, based on the amount of displacement detected by the detection part.
In addition, in the optical information recording device of the present invention, it is preferable that the gate signal designates the data recording starting position and the data recording ending position to be the starting position and the ending position in the data area of the recording reproduction surface where the front position of the sector is displaced most in a direction opposite to the scanning direction among the plurality of recording reproduction surfaces.
Furthermore, to achieve the above object, a fifth multilayer optical disc of the present invention is characterized in that the multilayer optical disc includes layers on which a plurality of recording reproduction surfaces are formed, with a sector structure having a gap area arranged between an address area and a data area in a scanning direction of an optical beam, bonded together such that front positions in the sectors of the respective recording reproduction surfaces are contacted closely to each other in the scanning direction by a predetermined precision, wherein guard data recording areas having a length of not less than the predetermined precision are allocated to a tip portion and to a back end portion of the data area in the scanning direction.
According to the configuration mentioned above, by determining the bonding precision between the plurality of recording reproduction surfaces to be not more than the predetermined length of the gap area or by determining the length of the gap area to be not less than the bonding precision between the plurality of recording reproduction surfaces of the multilayer optical disc, a recording operation for an arbitrary recording reproduction surface does not affect address areas in other recording reproduction surfaces, so that the address information can be recognized correctly after completing the recording at the time of reproduction.
Moreover, even when the plurality of recording reproduction surfaces are bonded together in a state in which they are not matched but shifted, by satisfying the relationship of Lxe2x89xa6G between the predetermined precision L corresponding to this amount of displacement and the length G of the gap area, matching the recording range for a certain recording reproduction surface with the data area, determining the recording range for other recording reproduction surfaces to be an area including a part of the gap area in addition to the most part of the data area, and recording while matching the data recording starting positions and the data recording ending positions in the plurality of recording reproduction surfaces, even in the case where the certain recording reproduction surface is already recorded, the recording for the other recording reproduction surfaces can be performed with a uniform recording power. Therefore, a non-uniform recording power can be prevented, and an amplitude difference in the reproduction signal of the data, that is, a S/N difference is suppressed, so that the recorded data information can be reproduced correctly.
Furthermore, even when the respective data areas in the plurality of recording reproduction surfaces have portions overlapping in the scanning direction, by providing guard data recording areas for data protection in the tip portion and the back end portion of the data areas, the reproduced data information is not affected even when there is an amplitude difference in the reproduction signal in these guard data recording areas resulting from the effective power difference in the recording beam, and therefore, correct reproduced data information can be obtained.